3.2.11 The Role of Haemoglobin

Question 1

Oxyhaemoglobin

Answer 1

• Each haemoglobin molecule has 4 haem groups
• each attaches to 1 oxygen
• 4 subunits, 2 alpha nd 2 beta
• Oxygen + haemoglobin = oxyhaemoglobin
• First oxygen bound makes conformational change so each O molecule binds easier (cooperative binding)
• Opposite happens when oxygen dissocaites

Question 2

How is CO2 transported in body?

Answer 2

• 5% in plasma
• 10% in carbaminohaemoglobin
• 85% as hydrogencarbonate ions

Question 3

How are hydrogen carbonate ions formed?

Answer 3

• CO2 leaves plasma and diffuses into RBCs
• CO2 reacts with H2O to form carbonic acid (H2CO3) (catalysed by carbonic anhydrase)
• H2CO3 dissociates into H+ and HCO3- ions
• HCO3- diffuses out of RBCs into plasma
• H+ ions lower pH of RBCs
• Changing the shape of haemoglobin’s tertiary structure hence its affinity for O2 decreases
• So H+ combines with haemoglobin to keep pH stable so haemoglobin acts as a buffer

Question 4

What is the chloride shift?

Answer 4

• As H2CO3 dissociates into H+ and HCO3-, H+ makes pH of blood low
• So Cl- ions diffuse into RBC to increase the pH and prevent electrical imbalance in RBC

Question 5

What is the bohr effect?

Answer 5

When CO2 is present, haemoglobin’s affinity for oxygen is lower because of the lower pH due to the H+ ions. So at higher partial pressures of CO2 haemoglobin’s affinity for O2 shifts to the left in the oxygen dissociation curve. So in respiring muscles with high concentrations of CO2, oxygen is dissociated more readily which provides working muscles with oxygen for respiration